Annotated record of the detailed examination of Mn deposits from the SO 79 (SEDIPERU - TUSCH) expedition from R/V Sonne

The research cruise SO79 with RV SONNE (April 18 to June 09 1992) aimed to assess the impact of a potential mining activity on the sensitive deep-sea ecosystem of the Peru Basin. Up to now only results of reconnaissance surveys of the extended manganese nodule field discovered in 1978 in the Peru Basin are available. The hydroacoustic, sedimentological, and geochemical studies on data and sample material of SO79 came to the following results: a small-scaled variation in thickness respectively type of surface sediments shown by the sediment echosounder respectively the side-scan-sonar is assumably due to variations in deposition or erosion. The composition of sediments is controlled by climatic cycles of different length which were caused by the variable influence of glaciation of the northern hemisphere. We think that during the quaternary a deep-water circulation reduced in intensity and O2-content may have produced a suboxic diagenetic environment which led to a remobilization and redeposition of Mn forming manganese nodules in the oxic surface sediments. Near the distinct redox boundary at about 10 cm depth the growth conditions for nodules are extremely favourable. Due to the great variability of sediments the impact of deep-sea mining will be highly variable and the disturbance of the seafloor will change the ecosystem considerably.